Break out the calamine lotion. As carbon dioxide levels rise with global warming, poison ivy may become even more prevalent and potent by the middle of the century. About 80% of people develop dermatitis after contact with urushiol, the plant's carbon-based active compound.

When exposed to elevated levels of carbon dioxide, poison ivy grew 149% faster than control plants and its urushiol became more allergenic, according to a 6-year experiment conducted at Duke University. Researchers say these findings were both unexpected and disturbing. Besides its potentially serious effect on human health, this more virulent poison ivy could also threaten forest ecosystems if it becomes overabundant.

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